This invention relates to a novel imaging system in which the recording material is selectively moved through a softenable medium under the influence of electrical forces, and particularly to fixing such migration images after they have been formed.
Recently, a migration imaging system capable of producing high quality images of high density, continuous tone, and high resolution has been developed. Such migration imaging systems are disclosed in copending applications Ser. No. 837,780, filed June 30, 1969, and Ser. No. 837,591, filed June 30, 1969. In a typical embodiment of that system an imaging member comprising a substrate, a layer of softenable material and photosensitive marking material is latently imaged by electrically charging the member and exposing the uniformly electrically charged member to a pattern of activating electromagnetic radiation such as light. The exposed marking particles migrate toward the substrate when the member is developed by softening the softenable layer.
"Softenable" as used herein is intended to mean any material which can be rendered more permeable thereby enabling particles to migrate through its bulk. Conventionally, changing permeability is accomplished by heat or solvent softening. "Fracturable" layer or material as used herein, means any layer or material which is capable of breaking up during development, thereby permitting portions of said layer to migrate towards the substrate or to be otherwise removed. The fracturable layer may be particulate, semi-continuous, or continuous in different embodiments.
There are other systems for forming the latent image, wherein non-photosensitive or inert, fracturable layers and particulate marking material may be used to form said images, as described in the aforementioned copending applications which also disclose a variety of methods which may be used to form latent images upon migration imaging members.
Likewise, various means for developing latent images in the novel migration imaging system are known. Typical developing means include solvent wash-away; solvent vapor softening, heat softening and combinations of these methods.
When certain development techniques are used in the migration imaging system of the present invention, the layer of softenable material may be substantially completely washed away, typically along the unmigrated marking material, leaving behind an image pattern of migrated marking material on the substrate. It has been found that the resultant image of marking material on the substrate may be in a fragile and easily damageable condition because the marking material is relatively loose and unfixed. This image is susceptible to smudging, scratching, smearing, or other undesirable defacing when handled by the human hand or when coming in contact with any abrasive instrument or other material. Such destructive displacement of the image of an imaged migration imaging member typically also reduces the physical and optical density of the desired image.
Such an unfixed migration image is useful in that it is observable and is a potential fixed migration image, but in its fixed conditions has the disadvantage of normally being unsuitable for use in any but delicate, non-contact applications which would preclude its use in hard copy applications such as microfilm.
Various methods and materials as well as combinations of methods and materials have previously been used to fix such unfixed migration images. For example fixing methods and materials previously used are disclosed in copending applications Ser. No. 590,959, filed Oct. 31, 1966, and Ser. No. 695,214, filed Jan. 2, 1968. However, in addition to the methods and materials previously used to fix such migration images, there is a continuing need for better methods and materials suitable for fixing such migration images.